Pulse control circuit



April 18, 1950 E. C. HARTWIG PULSE CONTROL CIRCUIT Filed Jan. 18, 1946WITNESSES:

D. C. Can ira/ Va/faye INVENTOR ATTORN Patented Apr. 18, 1959 PULSECONTROL @DIRCUIT Edward C. Has-twig", Pittsburgh, Pa, assignor toWestinghouse Electric (Corporation, East Pitts burgh, Pa, a corporationof Pennsylvania Application January 18, 1946, Serial No. 642,i4@

i611. sea en 1?) @laillcnsn This invention relates to an electroniccontrol circuit and has particular relation to a circuit for producingpeaked voltage impulses. In many control systems it is desirable to ourploy peaked voltage impulses for various purposes, such as the controlof electric valves of the are like type. For example, electronic controlsys= terns for resistance welders often employ peaked voltage impulsesin the control of thyrati'ons and particularly of thyratrons which areconnected in direct current circuits. 'Moreover, it is often necessarythat such voltage impulses occur at preselected phase positions withrespect to an alternating current voltage supply. in addition, it ismany times desirable that the phase position of the impulses beautomatically shifted ac cordance with a direct current controi voltagefor purposes of voltage compensation or current regulation.

One of the most widely used arrangements for producing peaked voltageimpulses is that employing a peaking transformer energized from thealternating voltage source. Such transformers are capable of deliveringa voltage impulse of very short duration relative to a half-period ofthe alternating voltage and having a relatively steep wave front.However, because of the well known characteristics of such peakingtransformers, it is not feasible to shift the phase of the voltageimpulse by more than 90 electrical degrees without switching theconnections thereof. These peaking transformers also require arelatively high power phase shifting circuit in association therewith.In addition, a great many practical difficulties are encountered if itis attempted to shift the phase of the voltage impulse produced by apeaking transformer automatically in accordance with variations in adirect current control voltage.

It is, accordingly, an object of my invention to provide a novel controlcircuit for producing peaked voltage impulses.

Another object of my invention is to provide a novel control circuit forproducing peaked voltage impulses having a preselected phase relationwith respect to an alternating voltage.

A further object of my invention is to provide novel apparatus forproducing peaked voltage impulses which vary automatically in phaseposition with respect to an alternating voltage in accordance withvariations in a direct current voltage.

A still further object of my invention is to provide novel apparatus forproducing peaked voltage impulses which may be varied in phase positionwith respect to an alternating voltage through a switch 2 oversubstantially a complete half period the alternating voltage.

The novel features of my invention are set forth with particularity inthe accompanying claims. The invention itself, however, together withits advantages and further objects thereof may be better understood fromthe following de scription of a specific embodiment thereof, when readin connection with the accompanying draw ing, in which the single figureis a schematic cir cult diagram of apparatus embodying my inven tion.

As shown in the drawing, the primary winding of a supply transformer iiis ene gized from pa r of alternating voltage supply lines 1 and Theprimary winding of an output transfer a capacitor ti and a pair ofelectric val and it are connected in series across the sec ary windingit of the supply transfe The electric valves 1 iii are preferably of thearc-like type, such thyratrons, and are connected to conduct current inopposite directions. Thus, the anode 25 of the first valve 11 9 isconnected to one terminal of the secondary winding l i of the supplytransformer 5, while the anode 27 of the other valve 2! is con nected tothe other terminal of the secondary winding i i and the cathodes 29 and3i of the two valves l9 and 2i, respectively, are connected together. Anasymmetrical conductor 33. such as a rectifier, preferably of the drytype, i connected in shunt with each valve. Each rectifier 33 isarranged to ofier its lower resistance to current flowing in a directionopposite to the direction of such current as may be conducted by thecorresponding one of the valves I9 and 2!. The primary winding 35 of anauxiliary trans= former 3'! is also energized from the alternatingvoltage supply lines '5 and 9. The secondary winding 39 of the auxiliarytransformer 31 is connected through a phase shifting circuit including acapacitor 4i and an adjustable potentiometer 43, to supply voltageacross a resistor 45, a potent-i=- ometer 4i and another resistor 49connected in series in the order named. Thus, an alternating voltage isimpressed across the series connected resistors 45 and 49 andpotentiometer 41 which is of the same frequency, but is displaced inphase with respect to the alternating voltage appearing across thesecondary winding ll of the supply transformer 5. The amount of phasedisplacement is determined by the adjustment of the potentiometer 43 inthe phase shifting circuit.

The control circuit of the first valve l9 may be traced from the controlgrid 5| thereof, through 3 a. grid resistor 53, the resistor 45 and thelefthand portion of the potentiometer 41 to the ad- Justable tap 55thereon and thence to the cathode 29. In tracing the circuit from theadjustable tap 55 on the potentiometer 41 to the cathode 29 of the valvel9, either of two paths may be followed, depending upon the position ofa doublethrow switch 51. If the switch 51 is in its lefthand position,the circuit is a direct connection from the adjustable tap 55 to thecathode 29. If the switch 51 is in its right-hand position, the circuitextends from the adjustable tap 55 through a resistor 59 and a portionof a voltage divider 6| to an adiustable tap 63 thereon and thence tothe cathode 29.

The control circuit of the second valve 2| may be traced from thecontrol grid 65 thereof through a grid resistor 81, the resistor 49 andthe right hand portion of the potentiometer 41 to the adjustable tap 55thereon and thence to the cathode 3! or the valve by either of the pathsjust described.

The resistor 59 and the divider 6! in the control circu ts of the valves59 and 2! are conne ted in a closed circuit in series with an auxiharyvalve s, preferably a vacuum tube, and a s1 able source of substantiallyconstant dicurrent voltage is connected in shunt with the volta edivider M. It then a pears that the vo tage across the resistor 59 andthe por= of divider iii in the control circuits of the main valves isand M de ends both in polar ity and ma nitude upon the magnitude of thecurrent conducted through the auxiliary valve 86.

The control circuit of the auxiliary valve iii? ext nds from the grid t9thereof through a grid resistor ill and a portion of another resistor 52to the cathode 75. A direct current control voltage from any suitablesource W is then applied across the resistor 13. It follows that thedirect current voltage su lied to the control circuits of the mainvalves 59 and 26 from the resistor 59 and the divider Si is varied inaccordance with variations in the direct current control voltage acrossresistor 73.

The o eration oi. the apparatus will be con sidered first when thedouble-throw switch V is in its lefbhand position. With the double-throwswitch 57 so positioned, an alternating volta e is impressed in thecontrol circuit of each of the valves is and 21 which is displaced inphase with respect to the alternating voltage appearing across thesecondary winding- H of the Sllnrfly transformer 5. This alternatingvoltage in the control circuit of either of the valves is and 2! becomesmore positive than the predetermined critical value necessary totenderthat valve conductive at an instant in a half-period of the alternatingvoltage appearing across the secondary winding ll of the supplytransformer 5, in which the anode of that valve is positive, whichinstant is determined by the adjustment of the potentiometer 43 in thephase shifting circuit.

After the hand switch 23 is closed, one of the main valves l9 and 2i isrendered conductive in the next half-period of the alternating voltageacross the secondary winding ii of the supply transformer 5. Theparticular valve to become conductive first depends upon the polarity ofthe next half-period following closure of the hand switch 23. If it beassumed that the polarity is such that the anode 25 of the first valve I9 is positive in the next half-period after closure of the switch 23,then the first valve I9 is rendered conductive at the preselectedinstant in that halfperiod.

When the flrst valve is becomes conductive,

current flows from the secondary winding H through the primary windingl3 of the output transformer 15, the capacitor ll, the first valve [9,the rectifier 33 in shunt across the second valve 2i and the hand switch23 back to the secondary winding ll. Since the capacitor I! has nocharge thereon when the first valve 19 becomes conductive, a surge ofcurrent of considerable magnitude flows through the primary winding i3of the output transformer 15 at that instant, causing the voltage acrossthe secondary winding 19 of the output transformer l5 to rise veryrapidly. The capacitor I! is of such size with respect to the voltageacross the secondary winding ll of the supply transformer 5 that it ischarged substantially completely in less than one-half period of thealternating voltage. Preferably the capacitor i1 is arranged to besubstantially completely charged in a time corresponding to about tenelectrical degrees. As soon as the capacitor i1 is substantiallycharged, the flow of current therethrough ceases so that the first valve59 becomes non-conductive and the voltage across the secondary winding19 of the output transformer i5 drops substantially to zero. As a resultof this operation, a very sharply-pealred impulse appears across thesecondary winding 19 of the output transformer {5 at the instant thefirst valve I9 becomes conductive.

In the next succeeding half period of the alternating voltage, thesecond valve 2i is rendered conductive at a presel cted instant. Thepreviously-charged capacitor I1 is then discharged through the secondvalve 2 I ,current flowing from the secondary winding H of the supplytransformer 5 through the hand switch 23, the second valve 2!, therectifier 33 in shunt with the first valve iii, the capacitor 11 and theprimary winding i3 of the output transformer i5 back to the secondarywinding H. The discharge of the capacitor ll plus the current from thesecondary winding ii again results in a surge of current charging saidcapacitor I! with an opposite polarity and producin a peaked impulseacross the secondary winding 19 of the output transformer E5 of oppositepolarity to the peaked impulse obtained in the previous half-period ofthe alternating voltage. The operation then continues with the first andsecond valves being rendered conductive alternately in opposite halfperiods of the alternating voltage.

It is to be understood that because the capacitcr i1 is charged in onehalf period, the voltage thereon tends to make positive the anode of thevalve to be rendered conductive in the next half period. Consequently,the anode of that valve actually is positive when the alternatingvoltage is zero at the beginning of the next half period. This enablesthe first and second valves to be rendered conductive at instantssubstantially corresponding to the zero voltage time of the alternatingvoltage to produce voltage impulses at those instants. Such anarrangement is sometimes highly desirable as in the system shown in mycopending application, Serial No. 642,041, filed January 18, 1946,embodying the apparatus of my present invention.

Although I have shown a particular phase shifting circuit in connectionwith the control circuits of the main valves l9 and 2|, it is to beunderstood that other suitable phase shifting circuits may be employedto permit the production of the peaked voltage impulses having anypreselected phase osition over substantially a complete half period ofthe alternating voltage supply.

When the double-throw switch 51 is in its righthand position, theoperation of the circuit including the secondary winding II of thesupply transformer 5, the capacitor H, the primary winding 53 of theoutput transformer 55, and the two main valves i9 and 2| remainssubstantially unchanged.

However, the instant at which the main valves it and 25 are renderedconductive is varied automatically in accordance with the direct currentcontrol voltage. For such operation, I prefer to have the alternatingvoltage appearing across the resistors 35 and E9 and potentiometer il,lagging behind the alternating supply voltage by approximately 65",although other phase displacements may be used if desired. This phaseshifted alternating voltage is superimposed on the direct currentvoltage appearing across the resistor 59 and the portion of the divider6! in the control circuits of the valves l9 and 2i. It is then' apparentthat variations in the direct current voltage cause the resultantvoltage impressed in the control circuits of the valves l9 and 2| becomemore positive than the critical value at an instant earlier or later inthe corresponding half period of the alternating supply voltage. Withthe alternating voltage across the resistors t and at and potentiometerQ'l lagging behind the supply voltage by approximately 65, it ispossible to vary the direct current voltage to cause each of the mainvalves iii and 25 to be rendered conductive at any pre selected instantwithin substantially a complete half-period of the alternating supplyvoltage.

Although I have shown a rectifier 33 in shunt with each of the mainvalves is and 29, it is to be understood that in some cases therectifier may be replaced by a suitable resistor or other impedancemember oilerlng a higher impedance to current than the correspondingvalve when it is conductive.

While I have shown and described a preferred embodiment of my invention,I am aware that many modifications thereof may be made with= outdeparting from the spirit of the invention. I do not intend, therefore,to limit my inven tion to the specific embodiment disclosed.

I claim as my invention:

it. Apparatus for producing peaked voltage impulses comprising an outputtransformer hav ing a primary winding and a secondary winding, acapacitor in series with said primary winding, means adapted to functionas a source of current, and means operable to form a complete conductiveconnection of said source across said series connected capacitor andprimary winding to charge said capacitor, the compo nents in saidcompletely conductive connection and said capacitor being dimensioned sothat said capacitor is rapidly chargeable to permit but an impulse ofcurrent therethrough.

2. Apparatus for producing peaked voltage impulses comprising an outputtransformer having a primary winding and a secondary winding, acapacitor in series with said primary winding, means adapted to functionas a source of alternating current, and means operable to form acomplete conductive connection of said source across said seriesconnected capacitor and primary winding for an interval in each half?period oi said source voltage beginning at a preselected instant thereinto charge said capacitor, the components in said completely conductiveconnection and said capacitor beingdimensioned so that said capacitor israpidly chargeable to limit the duration of current flow therethrough ineach half period to a time which is short relative to the duration of ahalf period.

3. Apparatus for producing peaked voltage impulses which vary in phaseposition in accordance with variations in a direct current controlvoltage, comprising an output transformer hav-- ing a primary Windingand a secondary winding, a capacitor in series with said primarywinding, means adapted to function as a source of alternating current,and means operable to form a complete conductive connection of saidsource across said series connected capacitor and primary winding for aninterval in each half period of said source voltage beginning at apredetermined instant therein to charge said capacitor, said operablemeans including means responsive to said control voltage for varyingsaid instant in accordance with variations in said control voltage, thecomponents of said completely conductive connection and said capacitorbeing dimensioned so that said capacitor is rapidly chargeable to limitthe duration of current flow therethrough in each half period to a timewhich is short relative to the duration of a half period.

l. Apparatus for producing peaked voltage impulses comprising meansadapted to function as an alternating voltage source, a capacitor, anoutput transformer having a primary winding a secondary winding, a pairof electric valves, valves, primary winding and capacitor beingconnected iii-series across said source with said valves being arrangedto conduct current in op posits directions, an assymmetrical conductorconnected in shunt across each of said valves and offering its higherresistance to current in the same direction as that in which current maybe conducted through the corresponding valve, and control meansconnected to said valves to cause each valve to become conductive for aninterval in each half period of the source voltage in which that valvemay conduct current beginning at a preselected instant therein, saidcapacitor being rapidly chargeable to limit the duration of current flowtherethrough in each half period to a time which is short relative tothe duration of a hall period.

5. Apparatus for producing peaked voltage impulses comprising meansadapted to function as an alternating voltage source, a capacitor, anout put transformer having a primary winding and a secondary winding, apair of electric valves, said valves, primary winding and capacitorbeing connected in series across said source with said valves beingarranged to conduct current in opposite directions, an impedance memberconnected in shunt across each of said valves and ofiering a greaterimpedance than the corresponding valve when it is conductive, to currentflow in the direction in which current may be conducted through saidcorresponding valve, and control means connected to said valves to causeeach valve to become conductive for an interval in each half period ofthe source voltage in which that valve may conduct current beginning ata preselected instant therein, said capacitor being rapidly chargeableto limit the duration of current flow therethrough in each half periodto a time which is short relative to the duration 01' a halt period,

6. Apparatus for producing peaked voltage impulses comprising meansadapted to function as an alternating voltage source, a capacitor, anoutput transformer having a primary winding and a secondary winding, apair of electric valves of the arc-like type, said valves, primarywinding and capacitor being connected in series across said source withsaid valves being arranged to conduct current in opposite directions, anassymmetrical conductor connected in shunt across each of said valvesand offering its higher resistance to current in the same direction asthat in which current may be conducted through the corresponding valve,and control means connected to said valves to render each valveconductive at a preselected instant in each half period of the sourcevoltage in which that valve may conduct current, said capacitor beingrapidly chargeable to limit the duration of current flow therethrough ina half period to a time which is short relative to the duration of ahalf period.

7. Apparatus for producing peaked voltage impulses comprising meansadapted to function as an alternating voltage source, a capacitor, anoutput transformer having a primary winding and a secondary winding, apair of electric valves, said valves, primary winding and capacitorbeing connected in series across said source with said valves beingarranged to conduct current in opposite directions, a rectifierconnected in shunt across each valve for conducting current in adirection opposite to that in which current may be conducted through thecorresponding valve, and control means connected to said valves to causeeach valve to become conductive for an interval in each half period ofthe source voltage in which that valve may conduct current beginning ata predetermined instant therein, said capacitor being rapidly chargeableto limit the duration of current flow therethrough in a half period to atime which is short relative to the duration of a half period.

8. Apparatus for producing peaked voltage impulses comprising meansadapted to function as a main alternating voltage source, a capacitor,an output transformer having a primary winding and a secondary winding,a pair of electric valves of the arc-like type, said valves, primarywinding and capacitor bein connected in series across said source withsaid valves being arranged to conduct current in opposite directions, anasymmetrical conductor connected in shunt across each of said valves andoffering its higher I resistance to current in the same direction asthat in which current may be conducted through the corresponding valve,and control means connectcd to said valves including means adapted tofunction as an auxiliary source of alternating voltage of the samefrequency but shifted in phase with respect to said main source voltageand means for adjusting the phase of said auxiiiary source voltage tocause each valve to become conductive at a pre-selected instant in eachhalf period of the source voltage in which that valve may conductcurrent, said capacitor being rapidly chargeable'to limit the durationof current flow therethrough in a half period to a time which is shortrelative to the duration of a half period.

9. Apparatus for producing peaked voltage imulses which vary in phaseposition in accordance with variations in a direct current controlvoltage comprising means adapted to function as an alternating voltagesource, a capacitor, an output transformer having a primary winding anda secondary winding, a pair of electric valves, said valves, primarywinding and capacitor being connected in series across said source withsaid valves being arranged to conduct current in oppoite directions, anasymmetrical conductor connected in shunt across each of said valves andoffering its higher resistance to current in the same direction as thatin which current may be conducted through the corresponding valve, andcontrol means connected to said valves to cause each valve to becomeconductive for an interval in each half period of the source voltage inwhich that valve may conduct current beginning at a predeterminedinstant therein and including means responsive to said control voltagefor varying said instant in accordance with variations in said controlvoltage, said capacitor being rapidly chargeable to limit the durationof current flow therethrough in a half period to a time which is shortrelative to the duration of a half period.

10. Apparatus for producing peaked voltage impulses which vary in phaseposition in accordance with variations in a direct current controlvoltage comprising means adapted to function as an alternating voltagesource, a capacitor, an output transformer having a primary winding anda secondary winding, a pair of electric valves of the arc-like type,said valves, primary winding and capacitor being connected in seriesacross said source with said valves being arranged to conduct current inopposite directions, a rectifier connected in shunt across each valvefor conducting current in a direction opposite to that in which currentmay be conducted through the corresponding valve, a control circuitconnected to each valve to render each valve conductive at an instant ina half period of the source voltage in which that valve may conductcurrent when a voltage more positive than a predetermined critical valueis impressed in said control circuit, and means for impressing in eachcontrol circuit an alternating voltage of the same frequency butdisplaced in phase with respect to said source voltage superimposed on adirect current voltage which varies in accordance with said controlvoltage whereby the impressed voltage becomes more positive than saidcritical value at an instant in a half period which varies with saidcontrol voltage, said capacitor being rapidly chargeable to limit theduration of current flow therethrough in a half period to a time whichis short relative to the duration of a half period.

EDWARD C. HARTWIG.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 2,294,671 Livingston Sept. 1,1942 FOREIGN PATENTS Number Country Date 519,481 Great Britain Mar. 28,1940

